Deciphering the geologic memory of a Permian conglomerate of the Southern Alps by pebble P–T estimates

摘要: The volcano–clastic sequence of Trompia Valley, which caps the Tre Valli Bresciane Variscan basement (TVB), comprises Dosso dei Galli Conglomerate (DGC), oldest deposit containing up to metre-sized metamorphic pebbles. This Lower Permian formation Basin was fed by erosion products chain. We used microstructural and mineral chemical data on pebbles DGC infer a quantitative tectono-thermal evolution eroded pre-Permian compare them with those TVB surrounding Southalpine units (tectono-metamorphic = TMUs). Metapelitic metaintrusive record polyphase metamorphism two re-equilibrations: first under epidote amphibolite facies (M1, \(T_{{\text{max}}} {\text{--}}P_{T_{\max } }\)) second greenschist (M2) conditions. Rock types largely match unit. structural records in are pre-Permian, conglomerate matrix is non-metamorphic. deposition age (283 ± 1–280.5 2 Ma) constrains minimal exhumation its source. lack staurolite bearing assemblages suggests that source already exhumed shallow levels (greenschist conditions) before thermal equilibration consequent upon continental crust thickening induced collision.